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.EPRINT  AND  CIRCULAR  SERIES 

OF  THE 

NATIONAL  RESEARCH 
COUNCIL 


INDEXING  OF  SCIENTIFIC  ARTICLES 


Bv  GORDON  S.  FULC; 

Corning  Glass  Works,  Corning,  New  York 


Including  an  Analytic  Index 
of  the  Astrophysical  Journal,  Vol.  51^54,  1920-1921 


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INDEXING  OF  SCIENTIFIC  JOURNALS 

BY  GORDON  S.  FULCHER 

The  importance  of  the  service  which  the  subject-indexes  of 
journals  may  render  to  scientific  research  is  not  generally  realized. 
Yet,  in  order  that  the  best  methods  may  be  chosen  and  unnecessary 
duplication  avoided,  each  research  should,  of  course,  be  based  on 
as  complete  a  knowledge  of  past  results  as  may  be  obtained;  and 
the  task  of  guiding  the  scientist  to  those  parts  of  the  enormous 
accumulation  of  scientific  literature  which  relate  to  his  work  natu- 
rally devolves  largely  upon  the  subject-indexes.  Also,  since  the 
greater  the  amount  of  time  and  effort  required  by  scientists  to 
secure  the  information  needed  for  effective  research,  the  greater 
will  be  the  proportion  discouraged  from  attempting  it  and  the 
greater  will  be  the  extent  to  which  the  research  done  will  be  either 
less  efficient  or  more  delayed  than  it  should  be,  therefore  the 
responsibility  resting  upon  these  indexes,  particularly  the  indexes 
of  abstracting  and  listing  journals,  to  perform  this  important  task 
well,  is  very  great. 

The  question  then  arises,  What  characteristics  must  the  indexes 
have  if  they  are  to  give  the  maximum  service  ? 

The  indexes  now  provided  are  of  various  types  and  degrees 
of  usefulness.  The  simplest  is  a  mere  unclassified  index  of  titles, 
which  are  arranged  alphabetically  by  their  significant  words.  The 
indexes  of  the  Astrophysical  Journal,  the  Physical  Review,  and 
many  other  journals  are  of  this  type. 

An  improved  type  is  the  classified  index  of  titles  in  which  the 
titles  are  arranged  under  a  limited  number  of  subject  headings  so 
as  to  bring  related  titles  together,  the  classification  being  based, 
however,  wholly  on  the  titles.  The  indexes  of  Science  Abstracts, 
Journal  de  Physique,  and  others  are  of  this  type. 

The  inadequacy  of  both  these  types  is  obvious  for  it  is  well 
known  that  in  most  instances  a  title  cannot  sufficiently  describe 
all  the  subjects  treated  in  the  article.  A  paper  on  "The  Atomic 
Weight  of  Iodine"  may  contain  results  relating  to  I2OS  and  to  the 
occlusion  of  oxygen  by  glass;  and  one  on  ''The  Flora  of  Formosa" 
may  describe  new  species  and  perhaps  new  genera. 


A  much  more  serviceable  type  is  the  index  of  titles  classified  by 
content  of  the  articles,  which,  while  retaining  the  titles,  recognizes 
their  shortcomings  and  classifies  each  with  more  or  less  precision 
under  headings  determined  by  an  examination  of  the  article  itself 
or  an  abstract.  Thus  "The  Flora  of  Formosa"  would  be  listed 
under  the  genera,  species,  and  other  subjects  concerning  which 
new  information  is  given.  The  International  Catalogue  of  Scientific 
Literature  and  the  cumulated  indexes  of  the  H.  W.  Wilson  Com- 
pany— Agricultural  Index,  Industrial  Arts  Index,  etc. — are  of  this 
character.  The  value  of  this  type  of  index  is  enhanced  if,  as  in 
the  case  of  the  Engineering  Index  and  the  card  indexes  of  the 
Concilium  Bibliographicum,  the  classified  titles  are  supplemented 
by  brief  statements  as  to  the  contents. 

Since,  however,  most  titles  are  incomplete  and  many  inaccurate, 
why  not  disregard  them  altogether?  This  is  done  by  the  content 
index.  In  preparing  it,  the  precise  subjects  dealt  with  in  each 
article  are  determined  by  an  analysis  of  the  original  or  of  a  reliable 
abstract,  index  entries  which  adequately  describe  these  contents 
are  formulated,  and  finally  these  entries  are  indexed  under  the 
proper  subject-headings,  alphabetically  arranged.  The  index  of 
Chemical  Abstracts  is  of  this  type,  being  based  on  an  analysis  of 
the  abstracts,  and  is  not  only  one  of  the  largest  but  also  one  of  the 
most  generally  useful  indexes  now  being  issued.  For  the  most 
part,  however,  the  classification  is  carried  through  one  stage  only, 
with  the  result  that  if  information  on  a  certain  phase  of  one  of  the 
larger  subjects  is  desired,  many  references  may  have  to  be  looked 
up.  Moreover,  the  index  depends  on  abstracts  which  vary  con- 
siderably in  their  standards. 

The  final  step  in  the  development  of  the  subject-index  is  to  base 
the  entries  directly — or  indirectly  through  abstracts — on  a  thorough 
analysis  of  the  original  articles,  and  to  carry  the  subclassification 
of  the  entries  through  two  or  three  stages  so  as  to  make  each  sub- 
division complete.  Since  the  articles  in  the  Astro  physical  Journal 
for  1920  and  1921  were  carefully  analyzed  in  preparing  the  analytic 
abstracts1  which  precede  the  articles,  it  was  possible  to  prepare 

1  Gordon  S.  Fulcher,  ''Scientific  abstracting,"  Science,  54,  291-95,  1921. 


from  them  a  very  thoroughly  classified  analytic  index.     This  is 
reprinted  at  the  end  of  the  paper. 

To  show  the  characteristics  of  the  analytic  index  as  compared 
with  those  of  two  types  of  title  index,  the  entries  used  by  each 
type  to  index  the  same  four  articles,  all  relating  to  photography 
(Astrophysical  Journal,  52,  86;  52,  98;  52,  201;  and  53,  349),  are 
collected  here: 

Index  of  the  Astrophysical  Journal 
(Unclassified  Title  Index} 

Contraction  and  Distortion  on  Photographic  Plates,  Image 
Image  Contraction  and  Distortion  on  Photographic  Plates 
Images,  Mutual  Action  of  Adjacent  Photographic 
Photographic  Images,  Mutual  Action  of  Adjacent 
Photographic  Plates,  Image  Contraction  and  Distortion  on 
Photographic  Sharpness  and  Resolving  Power 
Photometry  and  the  Purkinje  Effect,  Photographic 
Purkinje  effect,  Photographic  Photometry  and  the 
Resolving  Power,  Photographic  Sharpness  and 

Index  of  Science  A  bstracts 

(Classified  Title  Index] 
Photography 

Images,  Mutual  Action  of  Adjacent  Photographic1 

Photometry,  Photographic,  and  Purkinje-Effect 

Plates,  Photographic,  Image  Contraction  and  Distortion  on 

Resolving  Power,  Photographic  Sharpness  and1 
Vision 

Purkinje-effect,  and  Photographic  Photometry 

Analytic  Index2 
Photographic  plates;  properties 
contrast  functions 
drying,  time  of 
grain  size 
images 

contraction  and  distortion 
mutual  action 
sections 

1  These  references  are  put  in  by  analogy  with  the  others,  as  the  1921  index  has 
not  yet  been  issued. 

2  Headings  and  subheadings  alone  are  given;    see  the  complete  index  herewith 
reprinted  for  details. 


intensification 
penetration  of  light 
resolving  power 
sharpness 

shifts  of  spectrum  lines  and  star  images 
theoretical  relations 
turbidity 

Photometry,  photographic,  heterochromatic 
Purkinje  effect,  photographic 
Spectra 

measurements 

errors  possible 
shifts  of  lines 

photographic 
Stars 

measurements  from  photographs 

errors  possible 
Sun 

spectrum 

shifts  of  lines 
photographic 

The  precision  and  completeness  of  the  analytic  index  as  com- 
pared with  the  title  indexes  is  evident.  Moreover,  since  all  the 
results  relating  to  each  subject  are  indexed  together,  the  analytic 
index  also  provides  a  summary,  in  outline,  of  the  work  done  in 
each  field;  that  is,  the  reader  interested  in  a  particular  subject, 
such  as  clusters,  nebulae,  spectra,  variables,  can  determine  in  what 
phases  of  the  subject  progress  has  been  made  by  consulting  the 
proper  sections  of  the  index.  On  the  other  hand,  the  danger  of 
indexing  by  titles  alone  is  illustrated  by  the  classification,  in  the 
Index  of  Science  Abstracts,  of  the  reference  to  the  photographic 
Purkinje  effect  under  "Vision''  whereas  the  article  contains,  in 
fact,  no  reference  to  the  eye,  the  indexer  being  misled  by  the 
title. 

It  may  be  objected  that,  while  the  analytic  and  other  good 
content  indexes  are  clearly  more  useful  than  any  title  indexes,  they 
are  too  long  and  too  difficult  and  laborious  to  prepare.  But  a 
comparison  of  the  analytic  index,  here  reprinted,  with  the  corre- 
sponding four  separate  volume  indexes  of  the  Astro  physical  Journal 
shows  that  the  analytic  index  has  only  twice  as  many  words  as  the 


unclassified  title  indexes,  though  containing  three  times  as  many 
references,  which  are,  moreover,  precisely  and  thoroughly  classi- 
fied. Also,  the  preparation  does  not  require  remarkable  ability 
nor  should  it  take  an  undue  amount  of  the  editor's  time  if  the  work 
is  well  organized.  After  deciding  as  to  the  classification  to  be 
adopted,  the  editor's  task  is  merely  to  indicate  on  the  abstracts 
the  titles  to  be  used  to  index  the  articles  (heads  and  subheads 
being  designated  in  some  convenient  way)  and  later  to  go  carefully 
through  the  entries  which  have  been  typewritten  on  slips  and 
arranged  alphabetically.  The  clerical  work  can  be  greatly  simpli- 
fied by  the  use  of  methods  developed  by  such  indexing  agencies  as 
Chemical  Abstracts,  the  H.  W.  Wilson  Company,  and  the  New  York 
Times. 

The  subject-indexes  now  serving  the  various  sciences  vary 
widely  in  type  and  usefulness,  as  stated  above.  Some  are  very 
poor,  some  very  good;  but  none  is  as  complete  and  precise  as  it 
should  be  if  it  is  to  give  maximum  service  to  research  in  its  field. 
It  is  only  a  question  of  time,  however,  when  the  workers  in  each 
science  will  come  to  realize  the  incalculable  value  of  an  efficient 
abstract  journal  combined  with  a  complete,  precise,  and  thoroughly 
classified  subject-index,  and  they  will  arrange  to  make  the  small 
sacrifices  of  time  and  money  necessary  to  secure  such  uniquely 
important  tools. 

ANALYTIC  INDEX  OF  ASTROPHYSICAL  JOURNAL  FOR 

1920  AND  1921,  VOLUMES  51-54,  BASED  ON 

THE  ANALYTIC  ABSTRACTS 

For  references  to  spectra  and  spectroscopy  of  elements  and  compounds  see  Spectra. 

Absorption  of  light  Atmosphere  (see  also  Sky) 

by  atmosphere,  315-290  MM;  coefficients,  54,  297  absorption    of    light,    315-290  MM;     coefficients, 

by   vapors  in   King's  electric   furnace;    Kirch-  54,  297 

hoff's  law  applied  to,  51,  13  absorption    spectrum     (Fraunhofer    lines)     (see 

Aethylamine,  preparation  of;   method,  52,  129  Sun,  spectrum) 

Angles,  extremely  small;    interferometer  method  dispersion     of     light;      measurement;      stellar 

of  measurement,  51,  257  interferometer  method  suggested,  51,  263 

Arc  ozone  in;  amount,  daily  variations,  location,  and 

low-current;    anode  fall,  cathode  fall,  potential  suggested  origin,  54,  297 

and  potential  gradient  as  functions  of  cur-  Atomic  theory,  Bohr  (see  Spectra,  theory) 
rent,  to  i   amp.,  for  various  cathode  ma- 
terials  (Ag,   C,   Cd,   Cu,   Fe,   Sn,  Zn,  and  Benzene;  dispersion,  rotary  magnetic,  436-620  MM; 
salts  of  Ba,  Ca,  Cs,  Na,  and  Sr),  54,  273  54,  45 


Benzene,    nitro-;    dispersion,   rotary   magnetic, 

436-620  nn,  54,  45 
Binaries,  spectroscopic  (see  also  Variables) 

Boss  373,  elements  of  both  orbits,  parallax, 
and  proper  motion,  53,  201 

Boss  3644,  Virginis,  elements  of  orbit,  54,  226 

Boss  5026,  elements  of  both  orbits,  51,  187 

Boss  ssgi,  elements  of  both  orbits,  parallax, 
and  proper  motion,  53,  201 

+65036g  Camelopard,  radial  velocity,  52,  198 

a  Capella,  elements  determined  by  interfero- 
meter, 51,  263 

49  8  Capricorni,  elements  of  orbit,  54, 127 

12,  isK,  42,  and  50  Cassiopeiae,  radial  velocities, 
52,  198 

19  Cephei,  radial  velocity  variations,  51,  252 

13  Ceti,  binary  component;  elements  of  orbit, 
52,  no 

Class  Oes:  19  Cephei,  A  Cygni,  9  Sagittae,  and 
4  more;  radial  velocity  variations,  51,  232 

A  Cygni,  radial  velocity  variations,  51,  252 

X  Cygni  (Cepheid),  spectroscopic  orbit,  53,  95 

65  r  Cygni,  binary  component,  elements  of 
orbit,  53,  144 

34  f,  68,  71,  +62°i637  Draconis,  radial  veloci- 
ties, 52,  198 

205  Draconis,  elements  of  both  orbits,  parallax 
and  proper  motion,  53,  201 

dynamics;  tides  on  sphere  due  to  second  sphere 
rotating  around  it,  51,  309 

comp.  a  Hercules,  elements  of  orbit,  parallax  and 
proper  motion,  53,  201 

Lalande  29330  and  46867,  elements  of  orbit, 
parallax  and  proper  motion,  53,  201 

magnitudes,  absolute  (see  parallax) 

measurement  of  relative  brightness  and  position 
of  components;  interferometer  method, 
51.  257,  263 

orbits;  elements  of,  including  periods,  radial 
velocity  curves,  mass  functions  (see 
Boss  373,  3644,  5026,  559i;  <*  Capella, 
49  6  Capricorni,  13  Ceti;  X  and  65  T  Cygni, 
205  Draconis,  comp.  a  Hercules,  Lalande 
29330  and  46867,  OS  82) 

measurement  of;    interferometer  method,  51, 
257 

origin,  theory  of,  from  nebulae,  51,  309 

7r«  Orionis,  photometric  study,  51,  218 

02  82,  elements  of  orbit,  parallax,  and  proper 
motion,  53,  201 

parallax  and  absolute  magnitude  (see  Boss  373, 
5591;  205  Draconis,  comp.  a  Hercules, 
Lalande  29330  and  46867,  O2  82,  53,  201) 

proper  motion  (see:  Boss  373,  5591;  205  Dra- 
conis, comp.  a  Hercules,  Lalande  29330 
and  46867,  02  82,  53,  201) 

radial  velocity  (see  orbits,  also  +65  "369, 
Camelopard;  12,  isK,  42,  and  50  Cassio- 
peiae, Class  Oes;  34  <p-,  68,  71,  +62°i637 
Draconis,  21  IT  Ursae  Minoris) 


radiation  pressure  between  components,  theory, 

53,  i 

9  Sagittae,  radial  velocity  variations,  51,  253 
spectrum  of  Boss  2830,  comp.   a  Geminorum, 

and  W  Serpentis;   notes,  53,  13 
theory     (see    dynamics,  origin,  and  radiation 

pressure) 

zi  ir  Ursae  Minoris,  radial  velocity,  52,  198 
Binaries,  visual  (Double  stars) 

13  Ceti,  orbit,  52,  no  (see  Triple  systems) 

o  Hercules  and  comp.;    probably  optical  pair, 

53,  201 
measurement     of     separation,     photographic; 

possible  errors  due  to  mutual  action,  53,  349 
Brightness  (see  Clusters,  Comet,  Galaxy,  Magni- 
tudes, Nebulae,  Novae,  and  Sky) 
Brightness  ratio,  of  palladium  point  to  gold  point, 

Si,  244 

Camphor 

dispersion,  rotary;    magnetic  and  natural;   solu- 
tion in  ethyl  alcohol,  54,  116 
refractive    indices    for    1:1    solution   in   ethyl 

alcohol;   436-620/1**,  54,  116 
Carbon  disulfide;    dispersion,  rotary,   magnetic; 

436-620  MM,  54,  45 
Cathode,  for  vacuum  tube 
carbon,  limed;   preparation,  53,  323 

use  as  source  of  large  current,  53,  323 
Cathode  rays;  excitation  of  light  in  air;  intensity 

for  1500-3500  volts,  52,  278 
Cepheids  (see  Variables) 
Cluster  stars 

catalogue,  photometric  (colors  and  magnitudes) 
in  Messier  3,  848  stars,  51,  MO 
in  Messier  68,  56  giants,  51,  49 
colors  (see  catalogue) 

distribution    (number)  (see  M3   and   M68) 
relation  to  magnitude  (see  M.3  and  M68) 
variation  with  radial  distance  (see  Mi) 
giants  (see  M68) 

color;     relation    to   magnitude,   general   con- 
clusions, 51,  49 
magnitudes  (see  catalogue) 
distribution  (number)  (see  M3  and  M68) 
relation  to  color  (see  M3  and  M68) 
variation  with  radial  distance  (see  M.$) 
in  Messier  3;   photometric  analysis,  51,  140: 
colors  and  magnitudes 
catalogue  of  848  stars 
distribution    (number   of   each   color   and 

magnitude) 

distribution  in  space,   variation   with  dis- 
tance from  center 

relation  between  color  and  magnitude 
position  co-ordinates  of  370  stars 
variables,  17  probable 
in  Messier  53  (N.G.C.  5024);   variables 

positions  of  23  shown  in  photograph,  52,  73 
in  Messier  56  (N.G.C.  6779);  variables 
positions  of  3  shown  in  photograph,  52,  73 


Cluster  stars  (cent.) 
in    Messier    68    (N.G.C.    4590);     photometric 

analysis,  51,  49: 
giants,  colors,  and  magnitudes 
catalogue  of  56 
distribution    (number   of   each   color   and 

magnitude) 

relation  between  color  and  magnitude 
variables;    colors,  magnitudes,  positions,  and 

ranges  of  variation  of  28 
in  Messier  72  (N.G.C.  6891) 
comparison  stars,  magnitudes  of  29,  52,  232 
variables;     periods   and   light   curves  of   26 

Cepheids,  52,  232 

position  of  34,  in  photograph,  52,  73 
in  Messier  75  (N.G.C.  6864);  variables 

position  of  16,  in  photograph,  52,  73 
in  N.G.C.  7006  and  7789;   number,  52,  73 
number,  in  N.G.C.  7006  and  7789,  52,  73 
number    of    each    color    and    magnitude    (see 

Ms,  M68) 

variables  (see  MS,  53,  56,  68,  72,  75;  Variables) 
Clusters  (see  also  Cluster  stars) 
analysis,  photometric  (colors  and  magnitudes  of 

the  stars)  (see  Messier  3  and  68) 
brightness  of  average  cluster,  52,  73 
diameter,  of  N.G.C.  7006  and  7789,  52,  73 
form  of  Messier  68,  71,  49 
magnitude,  absolute  (see  parallax) 
Messier  3;  photometrjc  analysis,  51,  140 
Messier  8  (N.G.C.  6530),  photograph,  51,  4 
Messier  16  (N.G.C.  6611),  photograph,  51,  4 
Messier  22  (N.G.C.  6656),  photograph,  51,  4 
Messier  53  (N.G.C.  5024),  photograph,  52,  73 
Messier  56  (N.G.C.  6779),  photograph,  52,  73 
Messier  68  (N.G.C.  4590);  analysis,  photometric; 
form;     computed     parallax;     photograph, 

51,  49 

Messier  72  (N.G.C.  6981);    parallax,  52,  232; 

photograph,  52,  73 

Messier  75  (N.G.C.  6864);  photograph,  52,  73 
N.G.C.    7006;     diameter,    parallax    and    star 

counts,  52,  73 

N.G.C.  7492,  photograph,  52,  73 
N.G.C.    7789;     diameter;     number    of    stars, 

52,  73 

parallax  and  absolute  magnitude  (see  Messier 

68,  72;  N.G.C.  7006) 
average  cluster,  brightness,  52,  73 
computation,  methods,  51,  49 
globular  clusters,  forty,  52,  73 
photographs,  large  scale  (6o-inch) 

Messier   53,    56,    72,    75    and   N.G.C.    7492, 

showing  variable  stars,  52,  73 
Messier  68,  showing  variables,  51,  49 
in  Sagittarius  and  Scutum,  including  Messie 

8.  16,  and  22,  51,  4 
stars  in  (see  Cluster  stars) 

Colors     (see    Cluster   stars,    Novae,    Stars,  Vari- 
ables) 


Comets 

igigb;  brightness,  photographs,  behavior  of 
tail,  51,  103 

Morehouse's;  rejection  of  tail,  51,  103 

tail,  rejection  of;   instances  and  stages,  51,  103 
Constant  stars  (see  Stars) 
Cordoba  Observatory  Catalogue 

correction  for  position  of  star  12431,  51,  4 
Corona  (see  Sun) 

Dark  markings  (see  Nebulae,  dark) 
Diameters,  of  planetoids,  satellites  and  stars 

measurement  (see  Interferometer,  stellar) 
Discharge  through  gases 

occlusion  of  RaEm,  54,  285 
Dispersion 
by  atmosphere;    measurement;    interferometer 

method  suggested,  51,  263 

theory,  electron,  modified  to  include  variation 
with   temperature,    51,    223;     note   as   to 
priority,  53,  326 
Dispersion,  rotary     (see     Camphor,    Limonene, 

Sugar,  Tartaric  acid,  54,  116) 
Dispersion,    rotary,    magnetic     (see     Benzene, 
nitro-Benzene,  Camphor,  Carbon  disulfide, 
Ethyl     iodide,     Limonene,     a-monobrom- 
Naphthalene,  Sugar,  Tartaric  acid) 
theory,  electron,  extended 
isotropic  transparent  media,  54,  45 
optically  active  media,  54,  116 
Double  stars  (see  Binaries,  visual) 
Dynamics 

binary  system  (see  Binaries,  spectroscopic) 

single  mass,  rotating;    equilibrium,  51,  309 

potential  of  distorted  ellipsoid,  51,  309 

Eclipse  (see  Sun) 

Einstein  effect  (see  Gravitation) 

Electron  theory  (see  Dispersion  and  Dispersion, 

rotary,  magnetic) 
Electrons;    e/m    for    those    active    in    magnetic 

rotary  dispersion,  computed,  54,  45 
Emission  of  light,  in  discharge  tube 

intensity    as    function    of    energy    of    exciting 

cathode  rays,  52,  278 
Equilibrium  (see  Dynamics) 
Ethyl  iodide;  dispersion,  magnetic  rotary,  436- 

620  MM,  54,  4S 
Exploded  wire,  source  of  high  temperature  spectra 

(see  Spectra) 
appearance  and  mechanical  effects  (Plate),  51,  37 

Fluorine;  preparation  of  gas  by  electrolysis,  54, 133 
Furnace 

black  body,  double  platinum  wound,  51,  244 

electric  (see  Spectra) 

vacuum,  cathode  ray,  for  high  temperature,  53 , 
323 

Galaxy 

brightness,  surface,  as  viewed  from  distance, 
52, 162 


Galaxy  (conl.) 

comparison  with  typical  spiral  nebulae,  52,  162 
distribution  of  stars  in;   section,  52,  23 
origin;   theory,  51,  3og 
radiation  pressure  exerted  on  nebulae,  53,  r 
Giant  stars  (set  Cluster  stars  and  Variables) 
Gratings  (see  Spectra) 

polarizing  effect  on   reflected  and   transmitted 

light,  51,  129 
theory,    Rayleigh-Voigt;     evidence    confirming, 

Si,  129 
Gravitation 

attraction  on  nebulae  due  to  Galaxy,  53,  i 
Einstein    effect;      photographic    measurement; 
possible    error    due    to    mutual    action    of 
adjacent  images,  52,  98;   53,  349 
Majorana's  theory;   astronomical  consequences, 
54,  334 

Hydrogen;  production  by  high  potential  sparks, 
apparent,  52,  47 

Integral,  definite 

table  of  values  of    I    (t  -x,)n+%  cos  kx-dx,  53, 

»/o 
249 

Interferometer,  stellar  (Michelson's) 
description 

loo-inch;   accuracy  and  limits,  51,  263 
2o-foot;  construction,  adjust/nents,  and  pho- 
tographs, 53,  249 
modification  to  compensate  for  atmospheric 

dispersion,  51,  263;   54,  78 
effective  wave-length,  determination,  51,  263 
measurements 

a  Capella;    separation  and  positions  of  com- 
ponents, and  inclination  of  orbit,  51,  263 
theory  and  uses;    to  measure 

angles,    extremely    small,    and    changes    of 

angle,  51,  257 

diameters  of  planetoids,  satellites,  and  stars, 
51,    257;     also    distribution   of   luminosity 
on  the  disks,  53,  249 
dispersion  of  the  atmosphere,  51,  263 
parallaxes  and  relative  motions  of  stars,  51, 

257 

relative  brightness,  position,  and  separation  of 
double  stars  (binaries),  51,  257,  263 

Jean's  contributions  to  theory  of  cosmic  origins, 
5i,  309 

Kirchhoff's  law  (see  Absorption) 

Light  (see  Absorption,  Dispersion,  Emission,  Polar- 

•   ization,  Radiation,  Refraction,  Spectra) 
Limonene 

dispersion,  rotary,  magnetic,  and  natural,  436- 

620  MM,  54,  116 
refractive  indices,  436-620/4^,  54,  116 


Magnetic  rotary  dispersion  (sec  Dispersion) 
Magnitudes  (see  Binaries,  Clusters,  Cluster  stars, 

Stars,  Variables) 
Markings,  dark  (see  Nebulae) 
Mass,  constancy  of;  possible  influence  of  one  body 

on  the  mass  of  another,  54,  334 
Melting-point,  of  palladium,  51,  244 
Meteorites,  falling  into  sun;    light  to  be  expected 

from,  51,  37 
Molecular  models,  Bohr  type,  of  halogen  acids,  as 

basis  for  theory  of  band  structure,  51,  230 

Naphthalene,  a-monobrom-;  dispersion,  rotary, 

magnetic,  436-620  MM,  54,  45 
N.G.C.;    corrections  to  descriptions  and  positions 

of  various  nebulae,  51,  276 
Nebulae 

attraction,  gravitational,  by  Galaxy,  53,  i 
brightness,  surface,  of  nebulous  areas 

measurement,  photographic  method,  52,  162 
spirals;   results  for  well-known  nebulae  com- 
pared with  value  for  Galaxy,  52,  162 
catalogue,  descriptive,  of  330,  51,  276 
changes  in  X.G.C.  1555  and  2245,  51,  276 
constant  (unchanged);   N.G.C.  995,  1186,  2024, 

and  7023,  51,  276 
dark  clouds  or  markings;    photographs 

I.C.  II,  5146,  Cygnus;   unique  array,  51,  276 
N.G.C.  2146,  Camelopard,  51,  276 
near  f  Orionis,  including  Barnard  33,  53,  392 
in  Sagittarius  and  Scutum;  N.G.C.  6523  (M8), 

6611  (Mi6),  and  6618  (Mi?),  51,  4 
forces   acting   on;     electrostatic,    gravitational, 

and  radiative,  53,  i 

internal  motion  in  spirals  (see  Messier  51,  81) 
I.C.  431,  432,  and  434;   photographs,  53,  392 
I.C.  II,  5146,  Cygnus;    dark  markings;    photo- 
graph, 51,  276 

Messier  8  (X.G.C.  6523);    photograph,  51,  4 
Messier    16    (N.G.C.    6611);    photograph    and 

spectrum,  51,  4 
Messier  17  (X.G.C.  6618)  (Swan);   photograph, 

51,4 
Messier  51  (spiral);  internal  motion,  photograph, 

and  proper  motion,  54,  237 
MessierSi  (spiral);   internal  motion,  photograph, 

and  proper  motion,  54,  347 
X.G.C.  1555  and  2245;    changes  in,  51,  276 
N.G.C.    1700   and   3379;     radial    velocity   and 

spectrum,  51,  276 

N.G.C.  2023  and  2024;    photograph,  53,  392 
N.G.C.  2146;   photograph,  51,  276 
X.G.C.  2261   (Hubble),  theoretical  explanation, 

53,  169 

N.G.C.;    corrections  to   descriptions  and  posi- 
tions of  various  nebulae,  51,  276 
new;    descriptive  catalogue  of  255,  51,  276 
origin,  theory  of 

XT.G.C.    2261,    with    fan-shaped    appendage, 
53,  169 


Nebulae  (cant.*, 
origin,  theory  of  (cont.) 

planetary  nebulae,  by  collision,  54,  229 
spirals,  54,  347;   Jeans'  theory,  51,  309 
photographs,  large  scale  (see  I.C.  431,  432,  434; 
I.C.  II,  5146;    MS,  16,  17,  51,  81;    X.G.C. 
2023,  2024,  2146;    also  dark  clouds) 
near  f  Orionis,  53,  392 
in  Sagittarius  and  Scutum,  51,  4 
spirals;   N.G.C.  2146  and  15  others,  51,  276; 

MSI,  54,  237;   M8i,  54,  347 
misc.:  I.C.  I,  1470;  N.G.C.  1491,  2245,  2247, 

2294,  2359,  3379,  3384,  and  6888,  51,  276 
planetary,  origin;    collision  theory,  54,  229 
proper  motion  (see  Messier  51  and  81) 
radial  velocity 

explanations  suggested;   discussion,  53,  i 
X.G.C.  1700  and  3379,  51,  276 
radiation  pressure  on,  due  to  Galaxy,  53,  i 
spectrum  (see  Mi6;    N.G.C.  1700  and  3379) 
nebulosity  around  six  nebulous  stars,  52,  8 
spirals     (see     brightness,     catalogue,     internal 
motion,   new,   oiigin,   photographs,   proper 
motion) 

Swan  (X.G.C.  6618);    photograph,  51,  4 
theory  (see  X.G.C.  2261,  origin,  radial  velocity) 
effect  of  passage  of  a  star  near  or  through  a 

nebula,  53,  169;   54,  229 
types,  four;   examples,  53,  392 
variable  (see  changes) 

Nebulous  areas;    brightness  (see  Xebulae) 
Nebulous  stars  (see  Stars) 
Novae 

brightness  and  color  of  Persei  Xo.  2,  52,  183 
definition  suggested,  54,  229 
Ophiuchi   1919;   spectrum  and   radial   velocity, 

SI,    121 

origin,  collision  theory,  54,  229 
spectrum 
Ophiuchi    1919;    shifts   of   lines   and   bands, 

5I»  121 

shifts,  simple  interpretation,  51,  121 
theory  (see  origin) 

Occlusion,  of  RaEm  in  discharge  tubes,  54,  285 
Origin;    theory  of  (see  Binaries,  Galaxy,  Xebulae, 

Novae.  Solar  system,  Variables) 
cosmic  origins;    Jeans'  contributions,  51,  309 
Ozone,  in  atmosphere  (see  Atmosphere) 

Palladium,  melting-point,  51,  244 
Parallax  (see  Binaries,  Clusters,  Stars,  Variables) 
Photo-electric  cells 
alkali  metals  and  hydrides;    color  sensitiveness 

curves,  52,  129 

fatigue  tests  for  K  and  KH  cells,  52,  129 
preparation  of  Li  cell,  52,  129 
sensitiveness,   color,   for  30  cells,  including   all 
alkali  metals  and  hydrides  of  Xa,  K,  Rb, 
and  Cs,  52,  129 


Photo-electric  photometer,  for  stars 

description,  51,  193;    precision,  53,  105;   54,  81 
Photographic  plates;  properties 

contrast    functions   y   and    F;     variation    with 

wave-length;    Purkinje  effect,  52,  86 
drying,  time  of;  effect  of  exposure  on,  53,  349 
grain   size;     relation   to   sharpness,    theoretical, 

52,  201 
images 
contraction    and    distortion    during    drying, 

52,98 

mutual  action  of  adjacent  spectrum  lines  and 
stars;    analysis  of  effects  involved;    varia- 
tion with  exposure,  53,  349 
sections  of  star  images,  Plates.  52,  86,  98 
intensification;  effect  on  resolving  power,  52,  201 
penetration  of  light  of  different  wave-lengths, 

52,86 
resolving  power 

effect  of  intensification.  52,  201 
relation   to   grain   size   and   sharpness,   theo- 
retical, 52,  201 
variation  with  development  and  wave  length 

52,  201 
sharpness 

measurement;  improved  method,  52,  201 
relation  to  contrast  and  turbidity,  52,  201 
variation  with  development  and  wave-length 

52,  201 

shifts  of  spectrum  lines  and  star  images  due  to 
mutual    action    of    adjacent    images    (see 
images) 
theoretical    relations   for   resolving   power   and 

sharpness,  52,  201 

turbidity;   variation  with  wave-length,  52,  201 
Photographs  (see  Clusters,  Comets,  Xebulae,  Sun) 
Photometer  (see  Photo-electric  photometer) 
Photometry,  photographic,  heterochromatic;  dis- 
cussion and  warning,  52,  86 

Planetoids,  diameter;    measurement,  interferom- 
eter method,  51,  257 
Polarization 

measurement,  using  gratings;  warning,  51,  129 
produced  by  gratings,  reflected  and  transmitted 

light,  51,  129 

Prominences,  solar  (see  Sun) 
Proper  motion  (see  Binaries,  Xebulae,  Stars) 
Purkinje  effect,  photographic,  52,  86 

Quantum  theory  (see  Spectra) 

Radial  velocity    (see   Binaries,    Xebulae,   Xovae, 

Stars) 
Radiation 
constant    c>;     computed    from    gold   point    to 

palladium  point  ratio,  51,  244 
pressure 
on   atoms   and   electrons;     theory   based   on 

classical  dynamics,  52,  65 
between  binary  stars,  53,  i 
on  nebulae  due  to  Galaxy,  53,  i 


Radium  emanation  (Niton) 

occlusion  in  discharge  tube,  54,  285 
purification;   modification  of  Duane's  apparatus, 

54,  285 

Refractive     indices    (see    Camphor,     Limonene, 
Sugar,  Tartaric  acid) 

Satellites,  diameter;  measurement;  interferometer 

method,  51,  257 
Scandium,  carbide;    possible  formation  in  electric 

furnace,  54,  28 
Sky,  night;    brightness;    various  determinations; 

discussion,  52,  123 

Solar  corona  and  prominences  (see  Sun) 
Solar  system,  origin;  tidal  theory,  51,  309 
Spectra  and  spectroscopy 
absorption  spectra 

exploded  wire,  of  Fe,  X  2270-5645  A,  spectro- 
gram, 51,  37 

furnace,  electric,  of  Ba,  Ca,  Co,  Fe,  Ni,  and 
Ti;  variation   of   relative   intensities   with 
temperature,  51,  13 
production  of 

electric  furnace  spectra,  51,  13 
high    temperature    spectra,    extreme ;     ex- 
ploded wire  method,  51,  37 
theory  (see  halogen  acid  gases) 

Kirchhoff's  law  applied   to  electric  furnace 

spectra,  51,  13 

Zeeman  effect,  inverse  (see  Fe  and  V) 
air 

arc  spectrum;  two  new  lines,  54,  246 
spark  spectrum,  condensed 
effect  of  self-inductance  on  relative  intensi- 
ties, 590-872  MM,  Si»  236 
identification  of  Ar,  N,  and  0  lines,  590- 

872  MM,  Sit  236;   54,  76 
shift  with  reference  to  vacuum  tube  lines, 

Sit  236 

wave-lengths,  590-872  MM,  Sit  236;   54,  76 
ammonia     bands,     visible     and     ultra-violet; 

identification,  52,  301 

arc  spectra  (see  air,  Fe,  pole-effect,  pressure  shift) 

anode  and  cathode  spectra;   relative  behavior 

of    various    metal    lines;     variation    with 

atomic  weight,  54,  65 

comparison    with    furnace    spectra    (see    Ca, 

cyanogen,  and  Swan  bands) 
ionization  lines;  behavior,  54,  191,  246 
low-current;    variation  with  current;    excita- 
tion stages 

for  Ba,  Ca,  K,  Mg,  Na,  Sr,  54,  191 

for  Ag,  Bi,  Cd,  Cu,  and  Zn,  54,  246 

relation  of  results  to  Bohr  theory  and  Ritz 

equations,  54,  246 

standard  lines,  secondary;  comparison  of 
i2-mm  5-amp.  with  6-mm  6-amp.  arc, 
53,  260 

argon;  lines  in  condensed  spark  spectrum  in  air, 
590-872  MM.  51,  236;  54,  76;  shift  with 
reference  to  vacuum  tube  lines,  51,  236 


band  spectra  (see  ammonia,  cyanogen,  halogen 
acids,  Swan,  water,  C,  CO,  CO,,  CF4, 
HaS,  N,  SO,) 

arc  and  furnace  spectra;  comparison  of  in- 
tensity distribution;  CN  and  Swan  bands, 
53,  161 

Deslandres'  law;  test  with  nitrogen  positive 
bands,  52,  301 

theory  of  structure  of  infra-red  bands  (see 
halogen  acids) 

vacuum  tube  discharge  through   CO.,   HiS, 
NH4,  N,O,  N,O,,  and  SO,;    bands  excited 
in  visible  and  ultra-violet,  52,  301 
barium 

absorption  spectrum,  electric  furnace;  varia- 
tion with  temperature,  51,  13 

arc  spectrum,  low  current;  variation  with 
current,  54,  191 

classification  of  lines 

furnace  excitation,  infra-red,  51,  179 
low-current  arc  excitation,  54,  191 

infra-red  furnace  spectrum  to  856  MM,  at  vari- 
ous temperatures,  51,  179 

series  of  single  lines  and  triplets;    identifica- 
tion of  terms;   constants,  51,  23 
binaries  (see  Binaries) 
bismuth 

arc  spectrum,  low  current;  variation  with 
current,  54,  246 

classification  of  lines,  arc  excitation,  54,  246 

structure 

of  XX  4122,  4308,  4722;  Plate,  53,  323,  339 
of  XX  3397,  3511,  3596;  Plate  only,  53,  323 
of  X4722;  changes  in  relative  intensity  of 

components,  53,  339 
cadmium 

arc  spectrum,  low  current;  variation  with 
current,  54,  246 

classification  of  lines,  arc  excitation,  54,  246 

new  resonance  line,  X  3779,  54,  246 
calcium 

absorption  spectrum,  electric  furnace,  51,  13 

arc  spectrum,  low  current;  variation  with 
current,  54,  191 

classification  of  lines 

furnace  excitation,  infra-red,  51,  179 
low-current  arc  excitation,  54,  191 

furnace  spectra;  absorption,  emission  and 
mixed,  51,  13;  infra-red,  51,  179 

infra-red  furnace  spectrum  to  733  MM,  at 
various  temperatures.  51,  179 

new  lines,  fifty,  52,  265 

pressure  shifts  to  i  atm.,  315-650  MM,  53,  224 

series  of  singlets  and  triplets;    identification 

of  terms;   constants,  52,  265 
carbon 

bands,  negative;   origin,  52,  301 

band,  positive,  fourth;    wave-lengths,  52,  301 

ultra-violet  vacuum  spark  spectrum;  X  1931- 
360  A;  Plate,  52,  47;  wave-lengths,  53,  150 

X-ray  spectrum,  L-series;  identification,  52,  47 


Spectra  (con/.) 

carbon    dioxide;     bands   in   visible   and   ultra- 
violet, including  several  new,  52,  301 
carbon  monoxide;    bands  in  visible  and  ultra- 
violet; identification,  52,  301 
carbon     tetrafluoride;     bands    in    visible    and 

ultra-violet;    wave-lengths,  54,  133 
cathode  rays;    intensity  of  N  bands  excited,  as 

function  of  energy,  52,  278 
classification  of  lines 

enhanced  lines,  Fowler's;    discussion,  54,  246 
furnace  excitation  stages,  King's  electric; 
for  Ba,  Ca,  Co,  Xi,  and  Sr;  infra-red,  51, 179 
for  Mn,  X  2795-6500  A,  53,  133 
for  Sc,  X  3015-6559  A,  54,  29 
low-current  arc  excitation  stages 
for  Ag,  Bi,  Cd,  Cu,  and  Zn,  54,  246 
for  Ba,  Ca,  K,  Mg,  Na,  and  Sr,  54,  191 
comparison  with  furnace  classification,  54, 

246 
cobalt 

absorption  spectrum,  electric  furnace;    varia- 
tion with  temperature,  51,  13 
classification  of  lines;    furnace  stages;    infra- 
red to  809  MM,  51.  179 
infra-red    furnace    spectrum    to    809    MM,    at 

various  temperatures,  51,  179 
copper 
arc    spectrum,    low    current;    variation   with 

current,  54,  246 

classification  of  lines;    low-current  arc  stages 
and  comparison  with  furnace  stages,  54,  246 
continuous    background    obtained    with    ex- 
ploded wire  source,  51,  37 
cyanogen  bands 
intensity    distribution,    in    furnace    and    arc 

spectra,  53,  161 

X  3883  in  arc  and  furnace;   Plate,  53,  161 
excitation   of   spectra;   minimum    voltage;    he- 
lium spectra,  52,  i; 

variation  with  current  density;   helium,  52,  i 
exploded  wire  spectra  (extremely  high  tempera- 
ture absorption  and  emission  spectra) 
of  Cu,  Xi,  Mn;  continuous  background,  51,  37 
of  Fe;    absorption  spectrum,  X  2270-5645  A; 

Plate,  51,  37 

production,  method,  51,  37 
use  for  study  of  pressure  shift  suggested,  51,  37 
fluorescence  spectra  (see  mercury,  54,  149) 
fluorine;     spark    spectrum,    visible    and    ultra- 
violet, of  pure  gas;  wave-lengths,  54,  133 
Fraunhofer  lines  (see  Sun,  spectrum) 
furnace  spectra,  electric 
absorption  spectra  of  metallic  vapors 
comparison  with  emission  spectra,  51,  13 
production,  method,  51,  13 
theory";  Kirchhoff's  law  applied  to,  51,  13 
variation  with  temperature;   spectra  of 
Ba,  Ca,  Co,  Fe,  Xi,  and  Ti,  51,  13 
Ba,  Ca,  Co,  Xi,  Sr;   infra-red,  51,  179 
Mn,  280-820  MM,  53.  133 
Sc,  301-656  MM,  54»  28 


comparison  with  arc  spectra 
intensity  distribution  in 

cyanogen  and  Swan  bands,  53,  161 
spectra  of  Ba,  Ca,  Co,  Xi,  Sr,  51,  179; 

Sc,  54,  28 

comparison  with  solar  spectrum;   Sc,  54,  28 
effect  of  small  potential  gradient,  52,  187 
infra-red    absorption    spectra    to    920  MM,   of 

Ba,  Ca,  Co,  Xi,  and  Sr,  51,  179 
mixed     absorption     and     emission     spectra; 

production,  method,  51,  13 
origin  of  radiation;   discussion,  52,  187 
red  fringe;    explanation,  52,  187 
variation  with  temperature  (see  furnace  absorp- 
tion spectra) 

Zeeman  effect  for  iron  lines,  51,  107 
grating  spectrograph 

comparison  with  interferometer,  53,  260 
ghosts   and    reversals;     use   of,    in    accurate 

measurements,  53,  260 
intensity  effect  on  wave-length  nil,  53,  260 
polarizing  effect  on  reflected  and  transmitted 

light,  51,  129 

ultra-violet,  extreme,  52,  47,  286;   53,  150 
halogen  acid  gases  (HBr,  HO,  HF);    bands 
HC1  band  3.7  M;  wave-lengths,  law  of  spacing, 

evidence  of  satellites,  53,  300 
theory  of  structure  of  infra-red  bands 
isotopic  theory  of  doublets,  52,  248 
quantum  theory,  based  on  simple  molecular 

model  of  Bohr  type,  51,  230 
helium 
excitation     of     various     spectra;      minimum 

voltage,  52,  i 

intensity,  relative,  of  series  lines  and  bands  in 
arc  spectrum;   variation  with  voltage,  52,  i 
ultra-violet,  extreme,  spark  spectrum;   identi- 
fication of  lines,  52,  47 
hydrogen,  Balmer  series 

shift  of  Ha;    condensed   spark   in   air  com- 
pared with  vacuum  spectrum,  51,  236 
variations   in    relative   intensity   of   lines   in 
spectrum  of  Class  Md  variable  star,  53,  185 
hydrogen  bromide,  chloride,  and   fluoride   (see 

halogen  acid  gases) 
hydrogen  sulfide;  spectrum  of  discharge  through 

52,  301 
infra-red  spectra  (see  air,  Ba,  Ca,  Co,  Xi,  Sr, 

halogen  acid  gases,  sun,  water) 
elimination    of    scattered    light    of    shorter 

wave-lengths,  53,  121 
screen  for  light  to  7200  A,  53,  121 
interferometer  spectrograph 
comparison  with  grating,  53,  260 
ghosts   and    reversals;    use   of,   for   accurate 

measurements,  53,  260 
intensity  effect  on  wave-length  nil,  53,  260 
reduction  of  measurements,  method,  53,  260 
ionization  lines,  in  low-current  arc;    variation 
with  current,  54,  191 


Spectra  (con/.) 
iron 

absorption  spectrum 

furnace;  variation  with  temperature,  51,  13 

exploded  wire,  X  2270-5645  A;   Plate,  51,  37 
arc    lines,    \337o-67soA;     wave-lengths    of 

1026    lines,    measured    with    grating    and 

interferometer,  and  compared  with  Bureau 

of  Standards  results,  53,  260 
intensity  effect  for  arc  lines  nil,  53,  260 
pole-effect  in  Pfund  arc 

comparison  of   i2-mm   s-amp.   with  6-mm 
6-amp.  arc,  53,  260 

relation  to  Zeeman  effect  nil,  53,  320 
ultra-violet  spark  spectrum  to  200  A;    Plate, 

52,  47;  wave-lengths,  53,  150 
variations   in   relative   intensity   of   lines   in 

spectrum  of  Class  Md  variable  stars,  53,  185 
Zeeman  effect 

furnace  lines;    direct  and  inverse  effect  for 
100   lines;    camparison  with    results  for 
spark  lines;  Plates,  51,  107 
relation  to  pole-effect  nil,  53,  329 
isotopes,  components  due  to 
measurement     of     separation;      displaceable 

slit-method  suggested,  53,  329 
theory,  for  case  of  bands  of  HBr,  HC1,  52,  248 
magnesium 

arc    spectrum,    low-current;     variation    with 

current,  54,  191 
classification  of  lines;    low-current  arc  stages, 

54,  ioi 
manganese 
classification    of    lines,    280-650  MM;     furnace 

stages,  53,  133 
furnace  spectrum,  280-820  MM;   variation  with 

temperature,  53,  133 
measurements 

errors,    possible,    due    to    mutual    influence 
of  adjacent  photographic  images,    52,  98; 

53,  349 

of  shifts,  minute;    displaceable  slit  method, 

suggested,  53,  329 
of  ultra-violet  wave-lengths,  extremely  short, 

53,  150 

mercury;  fluorescence  spectrum,  excitation  of; 
active  molecules;  relation  to  exciting 
spectrum,  54,  149 

mixed  absorption  and   emission   spectra;    pro- 
duction in  electric  furnace,  51,  13 
nebulae;   spectra  (ses  Xebulae) 
neon;   low-voltage  spectrum  of  trace  of  neon  in 

helium,  52,  r 
nickel 

absorption  spectrum,  electric  furnace;    varia- 
tion with  temperature,  51,  13 
classification  of  lines,   furnace  stages;    infra- 
red to  780  MM.  51,  179 

infra-red    furnace    spectrum    to    920  MM;     at 
various  temperature?,  51,  179 


ultra-violet  spark  spectrum  to  731  A;    Plate, 

52,  47;   wave-lengths,  53,  150 
nitrogen;   band  spectrum 

excitation    by    vacuum     discharge     through 
N3O  and  NiOi,  52,  301 

intensity  as  function  of  energy  of  the  exciting 
cathode  rays,  52,  278 

new    ultra-violet    positive    bands    from    low- 
current  arc  in  air,  possible,  54,  246 

structure;    divergence  from  Deslandres'  law, 

52,  301 

wave-lengths  of  third  positive,  52,  301 
nitrogen;   line  spectrum 

identification  of  lines  in  condensed  spark  in 

air,  590-870  MM.  5i»  236;    54»  76 
relative   intensity;     effect   of   self-inductance 

with  spark,  51,  236 
shift  of  spark  lines  with  reference  to    vacuum 

tube  lines,  51,  236 
nitrogen     peroxide;      spectrum     of     discharge 

through,  52,  301 
nitrous  oxide;    spectrum  of  discharge  through, 

52,  301 

novae;  spectrum  (see  Novae) 
oxygen 

identification  of  lines  in  spark  in  air  and  Oa, 

590-870  MM,  51,  236;   54,  ?6 
shift  of  spark  lines  with  reference  to   vacuum 

tube  lines,  51,  236 
pole-effect 

in    iron    arc,    comparison    of    6-mm    6-amp. 

and  i2-mm  5-amp.  arcs,  53,  260 
measurement,    displaceable  slit-method    sug- 
gested, 53,  329 

relation  to  Zeeman  effect,  for  iron,  nil,  53,  329 
potassium 
arc    spectrum,    low-cunent;     variation    with 

current,  54,  191 
classification  of  lines,  low-current  arc  stages, 

54,  IQI 
pressure  shift 

calcium  arc  lines,  315-650  MM,  53,  224 
source  for  study;    exploded   wire  suggested, 

Si,  37 

in  stellar  spectra,  Arcturus,  Procyon,  53,  327 
quantum  theory  (see  theory) 
radium  emanation  (niton) 

new  lines,  398-745  MM,  54,  285 

relative  intensity  of  lines;    variation  during 

discharge,  54,  285 

resonance  lines  in  low-current  arc  spectra 
intensity  variation  with  current  for 
Ag,  Bi,  Cd,  Cu.  and  7,n,  54,  246 
Ba,  Ca,  K,  Mg,  Xa,  and  Sr,  54,  191 
Ritz  equations  (sec  series) 
scandium 

classification  of  lines,  furnace  stages,  54,  28 
furnace    spectrum,    301-656  MM;     at    various 
temperatures;    comparison  with  arc,  solar 
and  sun-spot  spectra,  54,  28 


Spectra  (cont.)  Swan  band 

scandium  (cont.)  intensity    distribution;      5165  A;     arc    and 

Zeeman  effect  for  lines  in  sun-spot  spectrum,  furnace  spectra,  53,  161 

54,  28  theory 

series  Bohr;    relation  of  low-current  arc  results  to, 

in  Ba  spectrum,  singlets  and  triplets,  51,  23  54,  246 

in   Ca    spectrum,   singlets  and   triplets,   52,  relation    of   minimum    voltage  results   for 

265  helium  to,  52,  i 

notation;   explanation,  51,  23  isotopic,  of  separation  of  doublets  of  HBr  and 

Ritz  equations;    relation  of  low-current  arc  HC1,  52,  248 

results  to,  54,  246  quantum,   of   structure   of   band   spectra   of 

shifts  of  lines  (see  spark  spectra,  Sun)  halogens,  based  on  simple  molecular  model 

measurement;    displaceable  slit  method  sug-  of  Bohr  type,  51,  230 

gested,  53,  329  titanium;  absorption  spectrum,  electric  furnace, 

photographic,  due  to  mutual  action  of  adjacent  at  various  temperatures,  51,  13 

images,  52,  98;  53,  349  ultra-violet  spectra  (see  Ca,  CO,  CO*,  F,  Mn,  X, 

silver  NIj4j  NlO,  N.O.,  SO,,  Sun) 

arc  spectrum,   low    current;    variation   with  extreme,  to   200  A   (see  C,  He,   Fe,  Xi,  Zn) 

current,  54,  246  measurements  of  wave-lengths,  53,  150 

classification  of  lines;   low-current  arc  stages,  source;   condensed  vacuum  spark,  52,  286 

54>  2-^°  spectrograph,  vacuum,  52,  47,  286;   53,  150 

screens  for  region  290-315  MM,  54>  2Q7 

arc   spectrum,   low   current;     variation   with  spectrograph,  special  double,  for  solar  spec- 
current,  54,  191  trum,  290-315  MM,  54,  297 
classification  of  lines;    low-current  arc  stages  vacuum  discharge  spectra   (see  CO,   CO=,  CF<, 

54.  iQi  X,  Xe,  XH4,  RaEm,  SO,) 

Zeeman    effect   for  D-lines;     explanation   of  intensity  of  X  bands  as  function  of  energy  of 

Woltjer's  observations,  51,  107  cathode  rays,  52,  278 

sources  of  light  (see  arc,  exploded  wire,  spark,  minimum  voltage  for  excitation  of  He  spectra, 

vacuum)  52,  i 

exploded   wire;     appearance   and  mechanical  spectra  of  discharge  through  CO*,  HiS,  XH4, 

effects  of  explosion,  51,  37  XaO,  XjOa,  SOj,  52,  301 

spark  spectra   (see  air,  argon,  fluorine,  hydro-  vacuum  sources 

gen,  nitrogen,  oxygen)  cathode   rays   from   treated  carbon  cathode, 

relative  intensity;  effect  of  self-inductance  on  used  to  heat  anode,  53,  323 

air  and  O  lines,  51,  236  condensed  spark,  52,  286 

shift  with  reference  to  vacuum  tube  lines;  air,  vanadium;    Zeeman  effect,   direct  and  inverse, 

Ar,  H,  X,  and  O  lines,  51,  236  for    90    furnace    lines;     comparison    with 

ultra-violet,  extreme  (see  C,  Fe,  He,  Xi,  Zn,  effect  for  spark  lines,  51,  107 

ultra-violet)  Venus;  spectrum  (see  Venus) 

spark,   condensed,   in    vacuum;     as   source   for  water    vapor;     absorption    band,    930-963  MM, 

extreme  ultra-violet,  52,  286  53,  121 

spectrographs  (see  grating,  interferometer)  X-ray  spectra 

standards,  international   secondary;    questioned  L-series  of  carbon;    identification,  52,  47 

lines  ;     comparison   of   6-mm    6-amp.   and  Zeeman  effect  (see  Fe.  Xa,  Sc,  V) 

i2-mm  5-amp.  arcs;   pole-effect,  53,  260  furnace  lines  compared  with   spark  lines,    of 

stellar  spectra  (see  Stars)  Fe  and  V,  51,  107 

strontium  relation  to  pole-effect  for  Fe  lines  nil,  53,  329 

arc-spectrum,    low-current;     variation    with  zinc 

current,  54,  191  arc   spectrum,    low   current;     variation   with 

classification  of  lines  current,  54,  246 

arc  stages,  low-current,  54,  191  classification  of  lines,  low-current  arc  stages, 

furnace  stages,  infra-red,  51,  179  54,  24& 

infra-red    furnace    spectrum    to    920  MM;     at  ultra-violet  spark  spectrum  to  316  A;    Plates, 

various  temperatures,  51,  179  52,  47,  286;   wave-lengths,  52,  286 

structure  (see  bands,  bismuth)  Stars 

sulfur  dioxide  bands  atmospheres,  pressure  in;  Arcturus  and  Procyon, 

in    visible    and    ultra-violet,    including    forty  53, 327 

new;   wave-lengths,  52,  301  binaries  (see  Binaries  and  Variables) 

sun  (sec  Sun)  brightness  (see  parallax) 


Stars  (cont.) 
catalogue  (see  Cluster  stars) 

in   Pleiades;     magnitudes  and  colors  of  821 

stars  in  region  2°  square,  54,  323 
spectroscopic    parallaxes,    magnitudes,    type, 

and  proper  motion  of  1646  stars,  53,  13 
Cepheids  (see  Variables) 

Class  Bo-Bs;  statistical  study  of  180  stars; 
mean  magnitude,  parallax  and  proper 
motion,  54,  140 

Class  O;  collision  theory  of  origin,  54,  229 
Class  Oes  (see  Binaries) 
Class  Md  (see  Variables) 
cluster  (see  Cluster  stars) 
colors  (see  Cluster  stars) 

determination  for  nebulous  stars,  52,  8 
nebulous  stars,  47,  including  p  Ophiuchi,  a 

and  22  Scorpii,  52,  8 
in  Pleiades;   753  dwarfs,  54,  323 
comparison  stars,  for  Messier   72;    photographic 

magnitudes  of  29,  52,  232 
constant  stars,  from  photometric  studies 
Bond  624,  53,  317 
i  and  a  Cassiopeiae,  54,  81 
Class  B:   ir<  Orionis,  £ ,  e,  and  /z  Tauri,  51,  193 
TT<  Orionis,  51,  193,  218 
£,  e,  and  ;t  Tauri,  51,  193 
/  and  TT  Persei,  53,  105 
radial  velocity  constant  (see  radial) 
density  of  stars 

in  Gal.  long.  +32°,  lat.  —20°,  52,  73 
in  Galaxy;   distribution,  52,  23 
in  space,  as  function  of  parallax  and  magni- 
tude, 52,  23 
diameters 

measurement  with  stellar  interferometer,  51, 

257  (see  Interferometer) 
a  Orionis,  53,  249 
disk  (see  diameter) 

darkening  of  limb  (see  Variables) 
distribution     of     luminosity;      interferometer 

method  of  study,  53,  249 
distribution  in  space  (see  density) 

number  of  each  magnitude  per  unit  volume, 

luminosity  curve,  52,  23 
double  stars  (see  Binaries,  visible) 
dwarf  stars,  in  Pleiades  (see  catalogue) 
Galaxy  (see  Galaxy) 
giants  (see  Cluster  stars,  Variables) 
magnitudes,  absolute  (see  parallax) 
magnitudes,  photo-electric,  of  j3,  S,  I,  w  Persei, 

53,  105 

magnitudes,  photographic  and  photo-visual 
catalogue,  of  1646  stars,  53,  13 
Class  Bo-Bs,  180  stars,  54,  140 
comparison  stars 

for  Messier  72,  29,  photographic,  52,  232 
for  Nova  Persei  No.  2,  36,  52,  183 
in  Messier  3  and  68  (see  Cluster  stars) 
in  Orion,  eight;   photo-visual,  53,  317 


in    Pleiades ;    statistical   study    of    821,    54, 

323 
scales,  photo-visual;  comparison  of  Barnard's 

with  Mount  Wilson,  54,  323 
measurements  from  photographs;  possible  errors 
due    to   contraction   effect,   52,   98;     and 
mutual  action  of  images.  53,  349 
nebulous  stars 
colors  of  47,  including  p  Ophiuchi,  a  and  23 

Scorpii,  52,  8 
spectrum 

R  Aquarii,  nebulous  lines;  Plate,  53,  375 
nebulosity  around  six  stars,  52,  8 
novae  (see  Novae) 
number  of  each  absolute  magnitude;  luminosity 

curve,  52,  23  (see  density) 
parallaxes  and  absolute  magnitudes 
catalogue  for  1646  stars;    spectroscopic  and 

trigonometric  results.  53,  13 
Class  Bo-Bs  stars;  mean  for  180,  54,  140 

Boss  1517,  51,  254 
determination;  methods 

accuracy,  relative;    discussion,  54,  140 
interferometer  method  suggested,  51,  237 
spectroscopic;  description,  53,  13 
distribution  of  stars  in  space  and  number  of 

each  magnitude,  52,  23 
relation    of    magnitude    to    space    velocity; 

statistical  study  of  1330  stars,  54,  9 
relation  of  parallax  to  apparent  magnitude 

and  proper  motion,  52,  23 
pressure  in  atmospheres  (see  atmospheres) 
proper  motion 

catalogue,  for  1646  stars,  53,  13 
Class  Bo-Bs,  mean  for  180  stars,  54,  140 
large;  two  faint  stars  near  MSI,  54,  237 
measurement;     interferometer    method    sug- 
gested, 51,  257 

radial  velocity  (see  velocity,  space) 
binaries  (see  Binaries) 

16,  19,  +S9°2395,  +83°I04  Cephei,  52,  198 
constant  for  S  Ophiuchi,  TJ  Serpentis,  ft  Pegasi, 

52,  3i7 

+73°835  Draconis,  52,  198 
a  Hercules  and  comp.,  53,  201 
25  8  Ursae  Majoris,  23  5  Ursae  Minoris,  52, 198 
spectra  (see  nebulous  stars) 
combined    bright    and    dark    line    spectra; 

explanation,  51,  13 
variable  (see  Variables) 
spectral  type 

catalogue  for  1646  stars,  53,  13 
theory;     effect   of   passage   of   a   star   near   or 

through  a  nebula,  53,  169;   54,  229 
origin  of  Class  O  stars,  54,  229 
variable  stars  (see  Variables) 
velocity;   radial,  tangential  and  space 

distribution;     frequency    of    each    velocity; 

statistical  study  of  1350  stars,  54,  9 
relation  to  absolute  magnitude,  54,  9 


'4 


Sugar,  cane;  aqueous  solution 
dispersion,  rotary,  magnetic  and  natural,  436- 

620  MM,  54,  116 
refractive   index,    one    to   one    solution,    436- 

620  MM,  54,  116 
Sun 

corona;  May  29,  1919;  photograph,  51,  i 
eclipse;  May  29,  1919;  Smithsonian  expedition; 

brief  report,  51,  i  (see  corona) 
meteorites  falling  into;    light  expected  from; 

theoretical  discussion,  51,  37 
prominence;  May  29,  1919;  photograph,  51,  i 
October  8,  1920;  very  high;  stages  of  growth; 

photographs  with  Ca  line,  53,  310 
spectrum,  including  Fraunhofer  lines 
comparison   with   arc   and   furnace   spectra; 

scandium  lines,  54,  28 
energy  distribution,  corrected  for  atmospheric 

absorption,  315-290  AIM,  54,  297 
infra-red,     890-990  up;      identification     and 
origin  of  lines;    wave-lengths -of  563  lines, 
including  50  solar;   also  Plate,  53,  121 
shifts  of  lines 

atmospheric  refraction,  53,  380 
center-arc,    predicted    by    anomalous    dis- 
persion theory,  54,  92 

mutual  influence  of  adjacent  lines;    data 
from  limb-center  comparisons,  54,  92  (see 
photographic) 
photographic  effect  of  adjacent  lines,  52, 

98;  53.  349 

theory,  anomalous  dispersion;    of  gravita- 
tional shift,  limb-center  shift,  and  mutual 
influence  shift,  54,  92 
spot  spectra  (see  spots) 
theory  (see  shifts) 
ultra-violet  (see  energy  distribution) 

map,  photographic;    315-290  MM,  54>  297 
spots 
spectrum 
comparison  with  arc  and  furnace  spectra; 

scandium  lines,  54,  28 
Zeeman  effect  for  scandium  lines,  54,  28 
theory;  cooling  of  rising  gases,  54,  293 
theory  (see  spectrum ,  spots) 

Tartaric  acid;  aqueous  solution 
dispersion,     rotary,     natural,     and    magnetic, 

436-620  MM,  54.  n6 
refractive  index,  for  one  to  one  solution,  436- 

620  MM,  54«  IJ6 

Telescope  objective;    diffraction  by;    effect  on 

image  of  disk  and  combination  of  disks, 

including  June;  mathematical  theory,  51,  73 

Temperature  scale 

brightness  ratio,  gold  point  to  palladium  point, 

5i.  244 

palladium  melting-point,  51,  244 
Theory  (see  Binaries,  Dynamics,  Electron,  Grat- 
ings, Gravitation,  Interferometer,  Nebulae, 
Novae,  Origin,  Photographic  plates,  Radia- 
tion pressure,  Spectra,  Stars,  Sun,  Variables 


Transits;    observation;    effect  of  diffraction  by 

telescope  objective;   theory,  51,  73 
Triple  systems 

65  T  Cygni;  orbit  of  spectroscopic  binary  com- 
ponent, 53,  144 

13  Ceti;  orbit  of  spectroscopic  binary  compo- 
nent and  perturbations  due  to  fainter  visual 
component,  52,  no 

light  curve  of  variable  binary  component  of 
X  Tauri,  51,  193 

orbits;  of  binary  components  (see  65  T  Cygni, 
13  Ceti,  and  X  Tauri) 

perturbations  due  to  third  body  (see  13  Ceti 
and  X  Tauri) 

X  Tauri;  photometric  study  of  variable  binary 
component;  orbit,  light  curve,  effect  of 
third  body  nil,  51,  193 

Variable  nebulae  (see  Nebulae) 
Variable  stars 

Algol;  photometric  study,  elements  of  eclipsing 
system,  light  curve,  color  of  satellite,  53, 
105 

R  Aquarii;  spectrum,  intensities  and  displace- 
ments of  lines  and  nebular  lines  (Plate),  53, 
37S 

•y  Argus;  spectrum;  temporary,  shifting,  absorp- 
tion He  lines,  52,  39 
7   Camelopardalis;     photometric    study;    light 

curve  and  elements,  54,  217 
RS  Canum  Venaticorum;  light  curve,  elements, 

computed  parallax,  53,  99 
/  Carinae;    periodic  variations  of  wave-length 

and  spectral  type,  54,  161 
i    H.    Cassiopeiae;    photometric    study;    light 

curve,  elements,  darkening  of  limb,  54,  81 
SX  Cassiopeiae;   light  curve,  elements,  53,  165 
T  Cephei;  periodic  spectrum  changes,  53,  185 
U    Cephei;     photometric   study;     light   curve, 
elements,  evidence  of  tidal  evolution,  52, 
145 

Cepheids  (see  I  Carinae,  X  Cygni,  Messier  72) 
light  curves  of  26,  in  Messier  72,  52,  232 
light  range,  small;    possibility  of    Cepheids 

with;  suggestion,  51,  62 
orbit,  spectroscopic,  for  X  Cygni.  53,  95 
origin;   collision  theory  of,  54,  229 
magnitude,  mean,  for  26  in  M?2,  52,  232 
periods;  in  M?2,  26  variables,  52,  232 

relation  to  spectral  type,  54,  161 
spectral  type;  range  of  variation  and  relation 

to  period,  54,  16 

spectrum;      periodic     variations     in     wave- 
length and  type;  /  Carinae,  54,  161 
theory  (see  origin) 
general  conclusions;    mean  atomic  weight; 

ratio  of  mass  to  radius,  52,  73 
relation  of  period  to  brightness,  52,  73 
variation 

binary  theory;   discussion,  51,  62 
condition  of;  ratio  mass  to  radius,  52,  73 


Variable  stars  (cant.) 

Class    Md;     spectrum;     periodic    changes    in 
emission   lines    (see    T   Cephei,    X   Cygni, 
R  Hydrae,  R  Leonis,  X  Ophiuchi,  R  Ser- 
pentis,  S3.  185;  R  Aquarii,  53,  375) 
classification  of  long-period  variables,  53,  179 
cluster  variables  (see  Cepheids) 
color  variation  of  typical,  51,  49 
colors  and  magnitudes  of  28  in  M68,  51,  49 
magnitude,  absolute,  of  typical,  51,  49 
new;   in  Ma;    17  probable,  51,  140 
in   Ms3,   56,   72,  and  75;    positions  of  80 

shown  on  photographs,  52,  73 
in  M68;   28,  mostly  typical,  51,  49 
colors  (see  cluster) 

satellite  of  Algol,  53,  105 
X  Cygni;  spectroscopic  orbit,  53,  95 
X  Cygni;   periodic  changes  of  spectrum,  53,  185 
darkening  of  limb;   i  H.  Cassiopeiae,  54,  81 
205   Draconis,  probable  eclipsing  variable,  53, 

201  (see  Binaries) 
eclipsing  variables 

light  curve  and  elements  (see  Algol,  y  Camelo- 
pardalis,  RS  Canum  Venaticorum,  SX 
and  i  H.  Cassiopeiae,  U  Cephei,  RT  Lacer- 
tae,  X  Tauri) 

probable,  205  Draconis,  53,  201 
ellipsoidal  variable  (see  ITS  Orionis) 
evolution,  tidal,  of  U  Cephei;   evidence,  52,  145 
giants  (see  Cepheids) 

R  Hydrae;   variations  in  spectrum,  53,  185 
irregular  variables;    collision   theory  of  origin, 

54,  229 
RT  Lacertae;    light   curve  and  elements,  52, 

257 

R  Leonis;   variations  in  spectrum,  53,  185 
light  curves  (see  Cepheids,  eclipsing,  ellipsoidal, 

and  long-period  variables) 
long-period  variables 
classification,  53,  169 
light  curves  of  66;   constants,  53,  169 
spectrum  of  R  Aquarii,  53,  375 
magnitude  (see  Cepheids) 


magnitude,  absolute  (see  cluster,  parallax) 
Messier  3,  53,  56,  68,  72,  75;   new  variables  (see 

cluster) 

Messier  72;  light  curves  of  26  Cepheids,  52,  232 
nebulous  variable  (see  R  Aquarii) 
new  variables  (see  cluster  variables) 

B.D.  +8i?27;    +8i?30,52,  145 
orbits;  elements  (see  eclipsing  variables) 

spectroscopic;  X  Cygni,  53,  95 
origin,    of    Cepheids    and    irregular    variables; 

collision  theory,  54,  229 

X  Ophiuchi;   variations  in  spectrum,  53,  185 
ITS  Orionis;   photometric  study;   light  curve  and 

elements,  51,  218 
parallax  and  absolute  magnitude,  of  RS  Canum 

Venaticorum,  53,  99 
periods  (see  light  curves,  Cepheids) 
photometric  study   (see  Algol,  y   Camelopard, 

i  H.  Cassiopeiae,  U  Cephei,  X  Tauri) 
TT<  Orionis,  constant  star,  51,  193,  218 
R  Serpentis;   variations  in  spectrum,  53,  185 
spectrum;    periodic  variations  in  emission  lines 
(see  R  Aquarii,  y  Argus,  Cepheids,  Class  Md) 
suspected  variables 
B.D.  +io?i77i,  52,  9 
Bond    624    in    Orion;     photometric    study; 

Hartwig's  elements  incorrect,  53,  317 
205  Draconis,  53,  201 
S  Persei,  53,  105 
X  Tauri;    photometric  study;    light  curve  and 

elements  for  binary,  51,  193 
theory  (see  origin) 

tidal  evolution;  evidence  of;   U  Cephei,  32,  145 
Wolf-Rayet  star  (see  y  Argus) 
Venus;  spectrum;  systematic  shifts  of  solar  lines; 
variation  with  zenith  distance;  explanation; 
Plate,  53,  380 

X-rays 

L-series  of  carbon;   identification,  52,  47 
source;  condensed  vacuum  spark,  52,  47 

Zeeman  effect  (see  Spectra) 


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